Anti-PECAM-1 antibodies: another tool for visualization of Reissner´s fiber and the subcommissural organ in rat central nervous system.

Reissner´s fiber (RF) is an extracellular structure formed by the condensation of material released by cells of the subcommissural organ (SCO). RF and SCO are involved in the morphogenesis of the central nervous system (CNS) in various species, from lower vertebrates to mammals. Visualization of RF and the SCO may be challenging due to the absence of markers and the limited number of commercially available antibodies (e.g., anti-SCO-spondin). In this work we present that anti-platelet endothelial cell adhesion molecule-1 (anti-PECAM-1) antibodies, which recognize the extracellular region of PECAM-1, bind to the RF and to the apical surface of SCO cells in rat CNS. According to our analyses, PECAM-1 represents previously unrecognized component of the RF, which is not produced by the SCO cells, but rather is incorporated into RF via SCO cells through as-yet-unknown mechanisms. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00429-026-03088-7.